1. Field
The present invention relates to wireless communication and, more particularly, to is a wireless communication system supporting multiple carriers.
2. Discussion of the Background
In general, a wireless communication system uses a single bandwidth to transmit data. For example, a 2nd-generation wireless communication system uses a bandwidth ranging from 200 KHz to 1.25 MHz, and 3rd-generation wireless communication system uses a bandwidth ranging from 5 MHz to 10 MHz. In order to support increasing transmission capacity, recently, LTE (Long Term Evolution) or IEEE 802.16m of 3GPP (3rd Generation Partnership Project) extends the bandwidth to 20 MHz or higher. To increase transmission capacity, increasing the bandwidth may be essential, but it is not easy to assign a frequency having a high bandwidth, except for some areas in the world.
A carrier aggregation (CA) technology aiming at obtaining an effect, as if a logically high band is used, by grouping a plurality of physically non-continuous bands in a frequency domain has been developed to effectively use fragmented small bands. Individual unit carriers grouped by carrier aggregation is known as a component carrier (CC). Each CC is defined by a single bandwidth and a center frequency.
A system in which data is transmitted and/or received in a broadband through a plurality of CCs is referred to as a multi-component carrier system (multi-CC system) or a carrier aggregation (CA) environment. The multi-component carrier system performs both a narrow band and a broad band by using one or more carriers. For example, when a single carrier corresponds to a bandwidth of 5 MHz, a bandwidth of a maximum of 20 MHz may be supported by using four carriers.
In order to operate the multi-CC system, various control signals are required between a base station (BS) and a terminal. For example, exchanging ACK (ACKnowledgement)/NACK (Not-ACKnowledgement) information for performing HARQ (Hybrid Automatic Repeat reQuest), exchanging CQI (Channel Quality Indicator) indicating downlink channel quality, and the like, are required.